Use the following method to determine the growth percent using basal area. This method can also be used to project basal area, diameters, and volume.

Procedure: Use a prism, bark gauge and a diameter tape to obtain growth information from a representative sample of trees (preferably all the trees within prism range at pre-selected points; for examle, every fifth point).

  The following information is obtained from each tree:
  
  a. Radial bark thickness
  b. Diameter at breast height (D.B.H. outside bark)
  c. Radial growth during the last 5 years (have the data or estimate it)
  

D.I.B. (D. Without bark) = D.O.B (D. With bark) - 2 X radial bark thickness.

d.i.b. = D.I.B. - 2 X radial growth during last 5 years

The term: Σ(d.i.b./D.I.B.)² is the ratio of basal area 5 years ago to the present basal area.

Example:

% growth = 1 - (Σ(d.i.b./D.I.B.)² /total trees in sample)
% = 1 - (3.105/5) = 1-.621 = .379
% = .379 or 37.9% (for 5 years)
% annual growth = 37.9/5years = 7.58%

Example: Estimated volume at end of 5 years:

Present volume/acre           = 1450 board feet
% growth in 5 years           = 37.9%
Increase in volume in 5 years = 550 board feet
Present volume/acre           +1450 board feet
Volume/acre at end of 5 years =2000 board feet